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dc.contributor.authorGaudin, Olivier Pierre Marie
dc.contributor.authorSamuel, Ifor David William
dc.contributor.authorAmriou, Samia
dc.contributor.authorBurn, Paul L.
dc.date.accessioned2020-03-23T12:30:03Z
dc.date.available2020-03-23T12:30:03Z
dc.date.issued2020-03-02
dc.identifier.citationGaudin , O P M , Samuel , I D W , Amriou , S & Burn , P L 2020 , ' Annealing-enhanced birefringence and aggregation in MEH-PPV : a spectroscopic ellipsometry study ' , Journal of Applied Physics , vol. 127 , no. 9 , 093101 . https://doi.org/10.1063/1.5096608en
dc.identifier.issn0021-8979
dc.identifier.otherPURE: 266336198
dc.identifier.otherPURE UUID: 4a1ce19d-0b95-4985-8ec2-81854c6e899e
dc.identifier.otherScopus: 85081134799
dc.identifier.otherWOS: 000519116200001
dc.identifier.urihttps://hdl.handle.net/10023/19695
dc.descriptionFunding: UK EPSRC (GR/S62628/01) and Royal Society Wolfson Research Merit Award (I.D.W.S.).en
dc.description.abstractWe have used absorption, photoluminescence (PL) and variable angle spectroscopic ellipsometry (VASE) measurements to investigate the structural changes that take place upon high temperature annealing in spin-coated films of the prototypical conjugated polymer (CP) poly[2-(2’-ethylhexyloxy)-5-methoxy-1,4-phenylenevinylene] (MEH-PPV). Absorption and VASE measurements reveal that the birefringence of the films increases by approximately a factor of two upon heating, which indicates significant increase in the alignment of the conjugated polymer (CP) strands within the film plane. Absorption and PL spectra indicate the formation in annealed films of interchain species having lower energy transitions. But these measurements alone do not reveal the type of interchain species formed, such as excimers or aggregates. VASE measurements were used to investigate this feature and clearly reveal a new, low energy, feature with a shoulder at 650 nm in the dispersion relations of the extraordinary (out-of-plane) extinction and absorption coefficients of annealed films, which we assign to aggregate absorption. Thus, our work shows that VASE is a sensitive enough technique to measure aggregate absorption in CP films. In the case of the ordinary (in-plane) extinction and absorption coefficients, there is increased amplitude of the lower energy peak upon heating, owing to increased uniaxial anisotropy, along with a broadening and a longer red-tail, but the well-resolved red-shifted absorption band seen for the extraordinary absorption coefficient, is not observed. Therefore, we conclude that while in-plane and out-of-plane aggregation occurs in annealed spin-coated films of MEH-PPV, aggregate absorption is only clearly observed when the aggregate electronic transition dipole is oriented preferentially in a direction perpendicular to the film plane. This conclusion is consistent with the usual observation that aggregate absorption in MEH-PPV films is not easily observed using absorption spectra alone, which are typically measured at normal incidence.
dc.language.isoeng
dc.relation.ispartofJournal of Applied Physicsen
dc.rightsCopyright © 2020 The Author(s).This work has been made available online in accordance with publisher policies or with permission. Permission for further reuse of this content should be sought from the publisher or the rights holder. This is the author created accepted manuscript following peer review and may differ slightly from the final published version. The final published version of this work is available at https://doi.org/10.1063/1.5096608en
dc.subjectQC Physicsen
dc.subjectTK Electrical engineering. Electronics Nuclear engineeringen
dc.subjectDASen
dc.subject.lccQCen
dc.subject.lccTKen
dc.titleAnnealing-enhanced birefringence and aggregation in MEH-PPV : a spectroscopic ellipsometry studyen
dc.typeJournal articleen
dc.contributor.sponsorEPSRCen
dc.description.versionPostprinten
dc.contributor.institutionUniversity of St Andrews. Centre for Biophotonicsen
dc.contributor.institutionUniversity of St Andrews. Condensed Matter Physicsen
dc.contributor.institutionUniversity of St Andrews. School of Physics and Astronomyen
dc.identifier.doihttps://doi.org/10.1063/1.5096608
dc.description.statusPeer revieweden
dc.date.embargoedUntil2020-03-02
dc.identifier.grantnumberGR/S62628/01en


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